An image forming apparatus (which is an example of an image processing apparatus) has been conventionally used. Regarding the image forming apparatus, an image forming apparatus has been known which forms images on both sides of a sheet and has a reversal mechanism for reversing a sheet. Regarding the image forming apparatus having the reversal mechanism, an image forming apparatus has been also known which forms an image on one side of a first sheet and then forms an image on a second sheet while reversing the first sheet and forming an image on the other side of the first sheet and has a standby mechanism for making the first sheet stand by until an image forming operation for the second sheet is completed. The image forming apparatus can effectively form images on both sides of a sheet by the reversal mechanism or standby mechanism.